Virsh migrate setmaxdowntime

Hi~
This is test module for virsh migrate-setmaxdowntime.

```
  NAME
    migrate-setmaxdowntime - set maximum tolerable downtime

  SYNOPSIS
    migrate-setmaxdowntime <domain> <downtime>

  DESCRIPTION
    Set maximum tolerable downtime of a domain which is being live-migrated to another host.

  OPTIONS
    [--domain] <string>  domain name, id or uuid
    [--downtime] <number>  maximum tolerable downtime (in milliseconds) for migration
```